Instrument child process field trial creation to measure success.
This will let us see how many clients are falling back to using
the command-line to synchronize state and also whether any of
them are failing to create field trials from shared memory or
command line.
Bug: 867558
Change-Id: If1dd1f694686a98b67a553344f3a3e2289424430
Reviewed-on: https://chromium-review.googlesource.com/1150505
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578036}